It is desirable to achieve both a greater aerodynamic efficiency and increased power output per unit weight for a gas turbine. Both efficiency and engine performance can be obtained by increasing the temperature of the hot working fluid. Theoretically, a gas turbine engine could operate at stoichiometric combustion ratios to extract the greatest possible energy from the fuel consumed. However, temperatures at stoichiometric and even non-stoichiometric combustion are generally beyond the endurance capabilities of traditional metallic gas turbine engine components.
The hot working fluid in the gas turbine engine results from the combustion of a fuel mixture within a combustor. Air is introduced through an opening in a combustor liner into the combustion chamber to provide the desired fuel mixture. In order to enhance the combustion process, many gas turbine engine designs utilise a metal combustor chute attached to the combustor wall. These are short length sections of tubes that help direct air from the outside of the combustor to the centre, thereby increasing the mixing effectiveness, which beneficially affects emission control and temperature traverse.
The chutes are typically manufactured by casting or by machining from a solid bar. The chutes are attached to the wall of the combustor through the use of a “top hat” flange that sits flush to the outer surface of the wall and internal welds which secure the chute in place.
The current manufacturing process of the chutes, by casting or machining is costly, time consuming, has a long lead time and is not responsive to possible changes in design parameters which may be specified during development. The method of assembly and forming the welds is similarly costly and requires specialist equipment.